Arc Flash Pressure Measurement by the Physical Method, Effect of Metal Vapor on Arc Blast

The effects of arc flash or arc blasts have received much attention in the electrical safety industry. Although many papers to date have focused on noise (auditory damage) and prediction of pressure, no consensus standard or unified method exists to predict the pressure or thermoacoustic blast created by an arc. There is strong belief in the industry that metal vaporization is a major contributor to the damaging effects and hazards of an arc blast. Our work was to determine if the effects of metal vaporization are the factor in the pressure and thermal hazards resulting from an arc blast. First, the relevant literature reviewed was to compare existing methods for practical measurements of arc blast pressure. Published methods were evaluated to determine if these may be suitable for prediction of pressure in enclosed equipment. To date, few papers provide practical equations that have the necessary parameters to accurately predict pressure that can be used to evaluate the switchgear failure or the effect on workers. The Crawford-Clark-Doughty paper appears to be the most promising. Second, we performed two types of controlled laboratory experiments to evaluate the effects of metal vapor expansion during an arc blast. This is commonly thought to be a significant factor in the pressure generated from an arc blast. The first experiment measured the displacement of an ejected door from which the acceleration and maximum velocity were calculated. The second experiment measured the pressure generated from an arc blast inside a closed box. The second experiment also served as a comparison to existing models. These experiments were done using two electrode materials.